In the following text, the term "instrument panel" is to be understood as meaning a shell structure which defines the visible side of a vehicle cockpit and generally bears control elements and display instruments. Vehicle cockpits with corresponding instrument panels are described, for example, in DE 34 47 185 A1 and EP 0 515 287 A1. In this prior art, the instrument panels comprise a supporting, dimensionally stable carrier part which, on the visible side, is generally laminated with a decorative plastic film. It is also customary to lay a foam cushion beneath the decorative film of the lamination, over the entire surface or in some areas, in order to achieve a pleasant handle (feel). The carrier parts are manufactured from different materials: rigid foam shells with a foamed-on lamination, injection-molded thermoplastic shells and shaped wood fiber parts are usual.
Since the introduction of the airbag, the instrument panel has had the additional role of covering the passenger airbag in a visually appealing form without limiting its function. There is an increasing demand for the airbag system to be impossible to pick out on the visible side of the instrument panel (so-called "invisible" airbag). For this purpose, the instrument panels have a U-shaped or H-shaped notch on the rear side in the opening area of the airbag, so that the expanding airbag can open one or two flaps. In this arrangement, either the material of the carrier part itself and/or a separately arranged component serves as a "plastic hinge". By way of example, please refer to DE 36 11 468 A1. The airbag system also includes a guide connection piece for the expanding airbag, the so-called ejection channel, which is usually a separate component which may be prefitted on the instrument panel. Manufacturing instrument panels as a thermoplastic injection molding makes it possible, with simple vehicle equipment, to dispense with lamination of the instrument panels, for example in favor of surface structuring (leather grain effect or the like). However, with unlaminated instrument panels there are difficulties with attaching additional elements, for example with prefitting an ejection channel for the airbag. Only those joining processes which do not form a disruptive presence on the visible side (adhesive bonding, welding) are suitable, thus limiting design and manufacturing options. In addition, a very wide range of requirements are imposed on the material properties of the instrument panel itself, of the ejection channel and the opening area for the invisible airbag. The instrument panel should not become brittle at cold temperatures, but should remain dimensionally stable at elevated interior temperatures; the material must therefore not be excessively flexible, while there are no excessively great demands placed on its tensile strength. On the other hand, the hinge area of the opening flaps of the invisible airbag system should be as flexible as possible, so as to be able to fulfill the appropriate function. The ejection channel should have a high strength and be rigid. The moduli of elasticity, the elongation at break and the tensile strength of said elements of an instrument panel with an invisible airbag are therefore required to differ greatly. In practice, materials which also differ are used, but this has the drawback of making recycling more difficult and more expensive. Furthermore, the lack of uniformity of the materials makes it more difficult to use unlaminated instrument panels, in which joining components using rivets or screws on the visible side is undesirable, even though the manufacture of thermoplastic injection moldings is economically beneficial and leaves a great deal of design freedom.